Where St James preached and spread the gospel after the Lord's ascension we have no account from the writers of the first ages of Christianity. According to the tradition of Spain, he made an evangelizing visit to that country, but the earliest known reference to this is only in the later part of the seventh century, and then in an oriental , not a Spanish source. ... He was buried at Jerusalem, but, again according to the tradition of Spain, dating from about 830, the body was translated first to Iria Flavia, now El Padron, in Galicia, and then to Compostela, where during the middle ages the shrine of Santiago became one of the greatest of all Christian shrines. The relics still rest in the Cathedral and were referred to as authentic in a bull of Pope Leo XIII in 1884.Pope Leo's bull would appear to coincide with the positioning of the relics in the silver casket that is now venerated in the Cathedral crypt.
The guide to the Cathedral, purchased in the bookshop, indicates that the Apostle was originally buried in a tomb that was part of a Roman cemetery, with the tomb on one level and an oratory above it. Over the centuries, this original construction has been lost. The present position of the tomb lies at the same level as the upper chamber or Oratory of the Roman construction. The practice of the pilgrimage to Compostela simply takes for granted the tradition that the Cathedral is indeed built on the site of the tomb of the Apostle James.
In terms of the image of St James that is represented by the tomb, it is one of an Apostle of Jesus Christ. It is the image of one who received from the Lord Jesus the message of salvation, one who preached that Gospel in the world, and the image of one who stands at the very beginning of the Christian tradition that is handed down in the Church to the present day.